This invention relates to magnetic bubble (domain) memories and more particularly to a driving circuit for forming a rotating in-plane magnetic field for bubble propagation.
As is well known in the art, magnetic bubble memories employ a magnetic field which propagates magnetic bubbles (domains) by a rotating in-plane magnetic field generated by two field coils oriented orthogonally to one another and physically encompassing the plane of movement of the bubbles. There are numerous examples of driving systems for the energization and de-energization of the field coils for providing the rotating field, most of which are L-C tuned circuits such as shown in the U.S. Pat. No. 3,763,478 to Yoshizawwa, having a circuit which resonants at the frequency of the power source to reduce driving power, the U.S. Pat. No. 3,934,235 to Bobeck, et al., showing a circuit for current phase relationship and for periodic refresh pulses; U.S. Pat. No. 3,720,883 to Hess, Jr. showing, interalia, a unit for generating a reversable magnetic field; the U.S. Pat. No. 3,879,585 to Bobeck, et al., utilizing a resonant L-C and class C driver circuits eliminating all series switching, a reference is also made to an article entitled "The Generation of Rotating Magnetic Field for Bubble Devices" by Vella-Coleiro, I.E.E.E. Transactions on Magnetics, Vol. Mag. 10; No. 3, Sept. 1974 (Pages 750-752) regarding resonant field coils and transistor switches.
All of the foregoing circuits, unfortunately, suffer from either high power consumption, circuit complexity or phase characteristics for the rotation frequencies of the drive field coils required in magnetic bubble memories; the poor phase characteristics being largely due to difficulty in initiating and terminating the current in the drive coils. This latter is important in view of the fact that as the frequency of bubble propagation increases, the bubble position on the propagate elements tend to lag behind the direction of the field vector due to the necessary field gradient required to drive the bubble, and the magnetization lag effects in the permalloy patterns.
It is an object of this invention to provide a reliable economic system for providing the current drive to the propagate field coils of a bubble memory device in which an easy start-stop operation and low power is inherent.
Another and more specific object of the invention is to provide a matrix rotating field drive circuit meeting the fundamental requirement that the magnetic field start-stop can be accomplished at pre-determined times and with the drive power remaining low and with the ability to tailor the rotating field to enhance operation margins and match the bubble propagation characteristics.
Another object of this invention appears to provide a bubble memory system drive which may be digitally controlled.
Still another object of this invention is to provide a drive system for a bubble memory where the control may be shared with a number of other devices.
Still another object of this invention is to provide a protection in the failure mode because of the means of introducing the energy into the drive system.